One of the principal mechanisms by which cellular regulation is effected is through the transduction of extracellular signals into intracellular signals that in turn modulate biochemical pathways. Examples of such extracellular signaling molecules include growth factors, cytokines, and chemokines. The cell surface receptors of these molecules and their associated signal transduction pathways are therefore one of the principal means by which cellular behavior is regulated. Because cellular phenotypes are largely influenced by the activity of these pathways, it is currently believed that a number of disease states and/or disorders are a result of either aberrant activation or functional mutations in the molecular components of signal transduction pathways. Consequently, considerable attention has been devoted to the characterization of these receptor proteins.
HER3 (also known as ErbB3), a member of the EGF family of receptor/tyrosine kinases, is a protein that has been shown to play a complex role in several signal transduction pathways by forming homo- and heterodimers with other members of the EGF family depending on their concentrations and the concentration of particular ligands. Unlike other members of the family, HER3 lacks an intrinsic kinase activity and must rely on the presence of HER2 to transduce the signal across the membrane. However, HER3 can bind ATP and can recruit SH2-containing proteins (Carraway, BioEssays, 1996, 18, 263-266). The two groups of ligands specific to HER3 and HER4 are collectively termed neuregulins (NRGs) because of their demonstrated role in the nervous system. HER3 and HER4 function as the binding receptors; and HER2 along with EGFR are considered co-receptors and are recruited as partners to HER3 and HER4 upon ligand binding. (Burden and Yarden, Neuron, 1997, 18, 847-855).
HER3, first cloned in 1989, was found in a variety of normal epithelial tissues as well as being overexpressed in human mammary tumor cell lines (Kraus et al., Proc. Natl. Acad. Sci. USA, 1989, 86, 9193-9197). It has also been shown to act in a variety of cellular signaling cascades including those involved in neural development (Britsch et al., Genes Dev., 1998, 12, 1825-1836), mammary morphogenesis (Alimandi et al., Oncogene, 1995, 10, 1813-1821), and phosphinositide 3-kinase p85 binding (Hellyer et al., Biochem. J., 1998, 333, 757-763). Disclosed in U.S. Pat. No. 5,183,884 and in the European Patent Application 0 444 961 A1 are the DNA encoding HER-3 as well as probes for HER-3, vectors encoding HER-3 and cell cultures expressing such vectors (Kraus and Aaronson, 1993; Plowman et al., 1991).
Manifestations of altered HER3 regulation appear in both injury and disease states, the most important being in the development of cancer. Cellular transformation and acquisition of the metastatic phenotype are the two main changes normal cells undergo during the progression to cancer. HER3 in cooperation with HER2 has been shown to be involved in the neoplastic transformation of cells (Alimandi et al., Oncogene, 1995, 10, 1813-1821). Recently, it has been demonstrated that HER-3 and HER-4 are expressed at high levels in gastric cancers with three out of six gastric cancers expression HER-3 and four out of six gastric cancers overexpressing HER-4 (Kataoka et al., Life Sci., 1998, 63, 553-564).
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of HER3. Consequently, there remains a long felt need for additional agents capable of effectively inhibiting HER3 function.
To date, strategies aimed at inhibiting HER3 function have involved the use of antibodies, antisense to the HER3 coreceptor, HER2, gene knockouts of HER2 and HER3 in mice and modifications to the ligands that bind HER3.
Studies using antisense to reduce the expression of HER2, the coreceptor of HER3 showed that reduced HER2 attenuated the effect of HER3 signaling but did not abolish it (Yoo and Hamburger, Mol. Cell. Endocrinol., 1998, 138, 163-171). Mice lacking HER3 die in utero due to the thinned and rudimentary development of the atrioventricular valves of the heart (Burden and Yarden, Neuron, 1997, 18, 847-855).
Therefore, it appears as though these targeting strategies are either lethal or lack specificity, thus warranting further development of entities capable of safely inhibiting HER3 function. Antisense oligonucleotides provide a promising new pharmaceutical tool for the effective modification of the expression of specific genes.